HermansCVR580
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Older Style 707 And 737 Engines

Wed Dec 26, 2012 2:20 pm

If you look at the front outer areas on the engines on 707 and older 737-200's they have what appear to be openings on the out side of the engines. What are they for? Can they be adjusted during flight?

Older 737-200
http://www.airliners.net/photo/Aer-L...d=622b9d5c895be3dc4df43b403d688aab

Newer 737-200
http://www.airliners.net/photo/Expre...d=c769f095bede66487a9c1a45be584520
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AF1624
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RE: Older Style 707 And 737 Engines

Wed Dec 26, 2012 4:00 pm

This is adjusted in flight simply my moving the throttle levers to a higher power setting. These doors open so that, basically, more air gets sucked in.

I'm sure someone will come up with a detailed explanation but that's the basics.

[Edited 2012-12-26 08:07:19]
Cheers
 
tdscanuck
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RE: Older Style 707 And 737 Engines

Wed Dec 26, 2012 7:11 pm

Quoting HermansCVR580 (Thread starter):
What are they for?

They're called blow-in doors. They allow more air into the inlet at low airspeed and high power. Old inlets didn't work well at low speed (low ram pressure) so they had auxiliary doors to let more air in when inlet pressure drops below ambient.

Quoting HermansCVR580 (Thread starter):
Can they be adjusted during flight?

Not directly. They're sprung doors and just respond to pressure changes across the inlet wall. They close up on their own when inlet pressure gets high enough (appropriate relationship of airspeed and engine thrust).

Tom.
 
HermansCVR580
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RE: Older Style 707 And 737 Engines

Wed Dec 26, 2012 7:42 pm

Very interesting, see I learn something new everyday.

So for example on the 737's some of the same planes that had these blow in doors in earlier pictures, then years later the exact same place no longer has them on the engine. Was the aircraft re-engined even though its still the older style straight pipe Pratts?
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timz
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RE: Older Style 707 And 737 Engines

Wed Dec 26, 2012 7:51 pm

Some early 747s had them too-- for some reason they could meet noise rules better without the blow-in doors and later 747s didn't have them. Maybe 737s were quieter without them too?

(Don't call 737 JT8Ds "straight-pipe"-- bypass ratio was around 1.)
 
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RE: Older Style 707 And 737 Engines

Wed Dec 26, 2012 7:53 pm

Quoting HermansCVR580 (Thread starter):
f you look at the front outer areas on the engines on 707 and older 737-200's they have what appear to be openings on the out side of the engines. What are they for? Can they be adjusted during flight?

They were also present on early 747s.


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dlednicer
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RE: Older Style 707 And 737 Engines

Wed Dec 26, 2012 8:29 pm

Blow-in (or more properly, suck-in) doors were also used on Spey-engined Phantoms (side of aft fuselage), Northrop F-5Es (side of aft fuselage), Dassault Mirages (side of inlets), IAI Kfirs (side of inlets), Sukhoi Su-22s (side of inlet), Su-27s (bottom of inlets), later model MiG-21s (side of fuselage ahead of wing), Mikoyan-Gurevich MiG-29s (top of inlets), Lockheed F-117s (top of inlets), General Dynamics F-111s (side of inlets) and many other military aircraft.
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DL_Mech
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 2:14 am

Here are the "sucker" doors in action:

http://www.youtube.com/watch?v=Sf3mo3QROC8
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Viscount724
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 2:56 am

More discussion of the "blow-in doors" in this 2007 thread.
737-200 Engine Modifications (by CTRL_ALT_DEL Jun 25 2007 in Tech Ops)
 
amccann
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 3:51 am

Quoting dlednicer (Reply 6):
Mikoyan-Gurevich MiG-29s (top of inlets)

I'm not positive, but I believe the inlets on the leading edge upper surface of the Mig 29 are auxiliary inlets used when the main inlets are closed to prevent the "injection" of FOD from the main inlets.


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rwessel
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 6:20 am

SR-71 too.


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HAWK21M
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 11:22 am

Quoting Viscount724 (Reply 8):

Thats a real oldie thread......

Auxiliary inlet doors were fitted to early JT8D's around the nose cowl. These were spring loaded and opened automatically whenever the pressure differential between inlet and external static pressures was high, ie slow speed, high thrust conditions (takeoff) to give additional engine air and closed again as airspeed increased causing inlet static pressure to rise.
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HermansCVR580
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 1:57 pm

Wow to me this is really amazing. I also never knew that military aircraft had these also, but after learning about them a bit they are a really simple device on a high tech engine. And to think now days there really is no need for them with the high bypass engines. We sure have come a long way.
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 7:33 pm

Quoting HermansCVR580 (Reply 12):
We sure have come a long way.

We sure have advanced a lot technology wise......but sadly the glory days of Aviation will never return.
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Viscount724
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RE: Older Style 707 And 737 Engines

Thu Dec 27, 2012 9:38 pm

JT3Ds on 707s and 720Bs had two types of blow-in doors.

This early version.


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And this later type mounted further forward on the nacelle.


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KC135Hydraulics
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RE: Older Style 707 And 737 Engines

Fri Dec 28, 2012 1:33 am

The E-8s here in the Deid also have these doors on them. An E-8 is basically a 707, and we've got the old engines on them. I've watched them a few times during engine run-ups/maintenance, and the doors definitely do not open and close symetrically! Some lag behind the others though they do all eventually open and close.
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JAGflyer
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RE: Older Style 707 And 737 Engines

Fri Dec 28, 2012 1:58 am

Here is a great video showing the doors moving on a 707.

https://www.youtube.com/watch?v=5dpFLssaSXw
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RE: Older Style 707 And 737 Engines

Sat Dec 29, 2012 8:30 pm

I never really knew how they worked either but then I sat next to them for an hour or so back in September and it was certainly a noise I won't soon forget! Here's a short video I took on my phone showing how they flap around on high power settings. I was fascinated watching them;

http://youtu.be/dnxgdKX6SzU
 
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 2:35 am

Quoting DL_Mech (Reply 7):

I find the suction vents on the Hawker Harrier very prominent.

Open;

http://3.bp.blogspot.com/-qKSAn7CIbns/T5TIHI6zm9I/AAAAAAAACJg/LlGCMnyv8mg/s1600/AV+8B+Harrier+II+Aircraft+4.jpg

Closed;


What the...?
 
tdscanuck
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 4:18 am

Quoting JoeCanuck (Reply 18):
I find the suction vents on the Hawker Harrier very prominent.

Harrier was a corner case because it had enormous thrust for its size and had to run at full thrust with zero (or even negative) forward airspeed. Even that giant inlet wasn't enough to move the requisite mass of air without blow-in doors.

Tom.
 
dlednicer
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 6:59 am

Quoting tdscanuck (Reply 19):
Harrier was a corner case because it had enormous thrust for its size and had to run at full thrust with zero (or even negative) forward airspeed. Even that giant inlet wasn't enough to move the requisite mass of air without blow-in doors.

The original P.1127 prototype even had inflatable inlet lips, to provide a better shape for high thrust/no speed operation:


The early prototype YAV-8Bs had two rows of blow-in doors to cope with these problems:
http://upload.wikimedia.org/wikipedia/commons/d/de/YAV-8B_Harrier_testing_a_ski_jump.jpg
 
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 7:25 am

Quoting dlednicer (Reply 20):
The early prototype YAV-8Bs had two rows of blow-in doors to cope with these problems:

I love how the pilot is leaning way forward in order to see over the nose.
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musang
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 1:09 pm

Quoting tdscanuck (Reply 2):
They're sprung doors and just respond to pressure changes across the inlet wall

To give an idea of how "sprung" they are, you can push them in manually.

(And while on the tangential subject of things you can do manually, you can lift the thrust reverser shutters on a DC-8-50!)

Quoting dlednicer (Reply 6):
used on Spey-engined Phantoms (side of aft fuselage), Northrop F-5Es (side of aft fuselage),

Interesting. If they're so far back, presumably they're not allowing air into the intake, but augmenting (adding) airflow into the exhaust duct?? Does the exhaust section demand more if after burning (reheating)?

Quoting Viscount724 (Reply 14):
JT3Ds on 707s and 720Bs had two types of blow-in doors.

The narrower type of door looks hinged at the rear, almost as if its a dump vent, i.e. letting air out. It would appear that this type forces the air to make an "s" turn into the intake.

Quoting KC135Hydraulics (Reply 15):
doors definitely do not open and close symetrically

Different spring pressure, hinge lubrication might contribute, but I'd contend that uneven vent opening would be likely due to the uneven pressure inside the intake, which I would further guess might be caused by airflow interference due to the proximity of the ground, and any crosswind. Most of that was conjecture!

Regards - musang
 
dlednicer
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 9:35 pm

Quoting musang (Reply 22):
Quoting dlednicer (Reply 6):
used on Spey-engined Phantoms (side of aft fuselage), Northrop F-5Es (side of aft fuselage),

Interesting. If they're so far back, presumably they're not allowing air into the intake, but augmenting (adding) airflow into the exhaust duct?? Does the exhaust section demand more if after burning (reheating)?

The engines on the F-5 are mounted very far aft, so the doors are at the inlet:
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musang
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 10:21 pm

Thanks for that, it sorts out the F-5. I had no idea they were so far aft.

However the Phantom doors are way aft of the engine face. Could they be to do with ventilation of the engine bay due to overheating of the RR Spey engines in the Royal Navy variant?

Regards - musang
 
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Francoflier
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RE: Older Style 707 And 737 Engines

Sun Dec 30, 2012 10:43 pm

Quoting TupolevTu154 (Reply 17):
Here's a short video I took on my phone showing how they flap around on high power settings.

Ouch, that fluttering can't be too good. I'm guessing the spring that counteracts the pressure differential is mostly worn in that case.
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ferpe
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RE: Older Style 707 And 737 Engines

Mon Dec 31, 2012 8:29 am

The blow in doors are there to help with the conflicting sizing requirements of the inlet at no or low speed and high speed. The problem is very well shown in the Harrier flow pictures, at low speed you need very broad and round lips as you are sucking air from a larger area then your inlet, even from behind the inlet lips at start. If the air does not follow the lip around to the inside you get inlet air separation which gives an airflow meeting the fan or compressor face which is uneven, can lead to surge.

At high speed it is the inverse, there is so much air available due to your forward speed stuffing air in the inlets that you can't consume all of it, ie you have air spilling over the sides of the inlet and if it does not attach around the outside lip you get drag. This problem is bad for an airliner (Inlet Mach range 0 to 0.85) but even worse for a fighter (Inlet should work over a Mach range 0 to 1.5).

For airliners advanced inlet lip shapes has given a good enough compromise so that you can do without the doors nowerdays, for fighters the Mach range is most of the time to large, especially if you have an inlet which has an optimized high Mach design like those with variable shock lips or bodies, these have almost invariably suck-in doors. Notable is that the JSF35 does not have doors (would cause radar reflections) or variable inlets (once again difficult to do with a low radar signature), therefore it has problems flying faster then M 1.5, today it better to be slower and not be seen then the opposite.
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HermansCVR580
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RE: Older Style 707 And 737 Engines

Mon Dec 31, 2012 1:38 pm

Do these blow in doors make the engines any more louder or do they have no effect on engine noise?
The right decision at the wrong time, is still a wrong decision. "Hal Carr"
 
Viscount724
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RE: Older Style 707 And 737 Engines

Mon Dec 31, 2012 8:06 pm

Quoting HermansCVR580 (Reply 27):
Do these blow in doors make the engines any more louder or do they have no effect on engine noise?

If not mistaken, one of the reasons they were eliminated on later engine versions was to reduce noise.
 
Gr8Circle
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RE: Older Style 707 And 737 Engines

Tue Jan 01, 2013 4:59 am

I remember doing a pre-flight walk around of an AI B707-337, and as he walked past the engine, he pushed in one of the blow-in doors on the P&W engine and shone his torch inside for a quick inspection........it just moved in easily, and swung shut on being released, as though it was held back in place by a spring.......
 
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HAWK21M
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RE: Older Style 707 And 737 Engines

Wed Jan 02, 2013 9:52 am

Quoting Viscount724 (Reply 28):
If not mistaken, one of the reasons they were eliminated on later engine versions was to reduce noise.

Franking speaking the noise reduction vide Noise supressors or Vortex generators may not be humanly noticeable due to the small variation in db levels.But exists when measured using test equipment.
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